The whole deal is of self preservation...our Shermans and especially the paperweight Stuarts put serious strains on the engines with all the track blocks they had hanging anyway they could get them to stay on, and had the blessings of the CO's. German tanks had thicker armor but poor designs in flat non angled armor and crews added anything they could get, including track blocks from other vehicles. Looking at all the variations, locations and improvised ways of fastening them, one can only assume the CO's allowed or suggested it. Now, with the advent of angled armor on tanks and modern anti tank ammo, it is a severe disadvantage to mount spare blocks, as they tend to trap the round and let it through, as opposed to deflecting it. That's considering standard armor piercing rounds....newer HEAT, shaped charge and super HV Sabot rounds will cut through anything you may have outside. Even in the 50's the trend was changing...I tried to mount extra blocks on the flat sides on my M-46 turret and was ordered to remove them, stating that exact reason. That's why the pistol port and side doors on turrets disappeared, as it weakended the armor at that point. Prior to my arriving in korea, some of the tanks had spare blocks hanging from the side stowage rails on the turret and the Easy 8 Shermans in a unit up the road had spare blocks on the bow plate,,but all came off.